Obesity is a major public health challenge and financial burden for most industrialised countries. In the United States, the healthcare costs for treating obesity reached more than $238 billion in 1999. The Centers for Disease Control and Prevention estimates that nearly 40 million American adults (about 20% of the adult population) are obese. The prevalence of obesity in the United States increased from 12% in 1991 to 19.8% in 2000. The situation is similar in European countries, where 10-20% of the men and 10-25% of the women are obese. “Clinically severe obesity,” defined, as being 100 or more pounds overweight, is associated with a number of serious and life-threatening health problems including diabetes, heart disease, respiratory problems, hypertension, gastroesophageal reflux disease, stress urinary incontinence, infertility, osteoarthritis, and some cancers. Conservative treatment, such as dieting, exercise and lifestyle changes, typically fails, making surgery the only hope for these patients. The surgical procedures are designed to restrict the size of the stomach so that food intake is limited and/or bypass steps in the normal digestive process (such as by connecting the stomach to a lower segment of the small intestine) so that food is either poorly digested or is rapidly passed. The National Institute of Health consensus conference in 1991 established widely accepted guidelines and indications for the surgical management of severe obesity (see Gastrointestinal Surgery for Severe Obesity: National Institutes of Health Consensus Development Conference Statement. Am J Clin Nutr 1992; 55: 615S-9S). Surgical methods currently in use are described below.
The relationship of gastric accommodation and satiety in obese individuals has been studied (see Independent Influences of Body Mass and Gastric Volumes on Satiation in Humans. Gastroenterology 2004; 126: 432-440). Increased body mass index has been associated with delayed satiation. Overweight and obese subjects ingest more at maximum satiation compared with normal weight individuals. Increased fasting gastric volume, however, was not associated with body mass index. Chemoreceptors and mechanoreceptors in the stomach wall signal satiation through vagal and splanchnic nerves. When the stomach is relaxed (increased volume at a constant pressure) within the physiological range, it requires higher increases in gastric pressure to activate stretch/tension receptors and thus induce symptoms such as satiation. Data suggests that satiation signals that inhibit ingestion are reduced with increased body mass and that is not due to increased capacity or the stomach's relaxation response to feeding. It has also been determined that the fasting volume of the distal stomach is greater in obese than control subjects (see Is There a Role for Gastric Accommodation and Satiety in Asymptomatic Obese People?. Obesity Research 2001; 9(11): 655-661). Gastric distention with eating contributes to the feeling of fullness or satiation. The mechanism is unclear, but distending the stomach stimulates gastric stretch receptors, which trigger vagal discharges that activate hypothalamic neurons and induce the feeling of satiety. Peptides like leptin, cholecystokinin, and glucagons-like peptide 1 have been shown to evoke satiety, thereby reducing food intake.
The Roux-en-Y gastric bypass is used for surgical treatment of morbid obesity. This involves the partitioning the upper stomach with a surgical stapler and creating a 15 cc intact pouch along the lesser curvature of the stomach. After bypassing a 100 cm section of the bowel, the small intestine is attached to the gastric pouch.
Vertical banded gastroplasty is a simpler operation that involves only the creation of a gastric pouch but does not require extensive surgery of the small intestine. In this procedure, biomaterials that are sutured around the lumen to control stoma size and prevent late stretching of the opening. Biomaterials that are currently used for this procedure include Bard Mesh (C.R. Bard, Inc., Cranston, R.I., USA) and PeriStrips (Biovascular, Inc., St. Paul, Minn., USA).
Another technology used in bariatric surgery is laparoscopic banding. Gastric bands are commonly used to facilitate a reduction in food consumption. The bands are placed around the upper part of the stomach to create a small gastric pouch that limits food consumption and creates an earlier feeling of fullness. Some bands are inflated with saline and connected to an access port placed close to the skin that allows the band to be adjusted. Although the devices are intended to remain in place permanently, the procedure is completely reversible and does not require transection or stapling of the stomach and re-routing of the gastrointestinal tract.
Gastric bands have been developed and are commercially available. For example, Lap-Band™ is an implant that is made from silicone (Inamed, Santa Barbara, Calif., USA; see also U.S. Pat. No. 5,074,868; U.S. Pat. No. 5,226,429; U.S. Pat. No. 5,449,368; U.S. Pat. No. 5,910,149). The SAGB™ or Swedish Adjustable Gastric Band (Obtech Medical AG, Zug, Switzerland) is an inflatable device made of silicone reinforced with a textile.
Gastric pouches were developed by Wilkinson (see U.S. Pat. No. 4,403,604; U.S. Pat. No. 5,246,456). Gastric reservoir reduction was accomplished by wrapping the stomach with an inert fabric. The purported advantages of the gastric pouch include maintenance of restricted size, early satiety with eating, and passage of food through the whole intestine. Gastric wrapping has been shown to create excess body mass index loss of 49, 66, 73, and 66 percent at 6, 12, 24 and 60 months respectively (see A Comparison of the Gastric Bypass and the Gastric Wrap for Morbid Obesity. Surg. Gynecol. Obstet. 1993; 176: 262-266).
Electrical pacing has been applied with benefit in many areas of surgery. In the treatment of obesity, gastric myo-electric stimulation has been shown to produce satiety. Gastric pacing has been shown to create excess body mass index loss of 18.8, 24.1, 22.3, and 32.6 percent at 6, 12, 24 and 60 months respectively (see Gastric Pacing as Therapy for Morbid Obesity: Preliminary Results. Obesity Surgery 2002; 12: 12S-16S).
Each of the implants and procedures presently in use has one or more deficiencies. For example, their construction can result in characteristics that increase the risk of leakage, acute gastric dilatation, wound infection/seroma, obstruction, stoma narrowing/stenosis (with persistent vomiting), ulcer, band slippage or erosion, reservoir deflation/leak, anaemia, calcium deficiency/osteoporosis, and vitamin and mineral deficiencies. Additional disadvantages include the presence of a foreign body, possible difficulties with reversibility if needed, and the increased operative time required to complete the more difficult procedures. The procedures described above can also result in extended patient stay in the hospital due to the invasive nature of the procedures. Also, there is a 19% risk of incisional hernia post-operatively when the procedure is performed by open surgical techniques.
Accordingly, there remains a need for implants for treating obese patients and methods of making those implants.